Converting carbon oxides in gas phase fluids

ABSTRACT

A process for reducing the carbon oxide content in natural gas, by producing a carbon oxide containing natural gas from a geological formation through a natural gas delivery system; providing a reaction zone containing at least one catalyst suitable for hydrocarbon conversion in the natural gas delivery system; introducing hydrogen into the carbon oxide containing natural gas to form a reaction mixture; and passing the reaction mixture to the catalyst in the reaction zone to convert at least a portion of the carbon oxides in the natural gas to hydrocarbons.

FIELD OF THE INVENTION

The present invention is directed to a system and process for removingcarbon oxides, including carbon monoxide and carbon dioxide, fromnatural gas.

BACKGROUND OF THE INVENTION

Natural gas fields that are currently being produced frequently containacid gases, in addition to the methane and decreasing amounts of higherhydrocarbons that are normally associated with natural gas production.Acid gases which are often encountered include one or more of CO₂, CO),hydrogen sulfide, carbonyl sulfide, carbon disulfide, mercaptans,sulfides and aromatic sulfur compounds. Processing and handling naturalgas that contains acid gas contaminants present corrosion, handling andenvironmental problems that are generally addressed with high costequipment and special procedures, often with additional energy costsinvolved.

Natural gas fields containing high amounts of carbon oxides areparticularly costly and difficult to produce. Natural gas fields thatcontain greater than 70 vol. % carbon oxides are known. Low temperatureliquefaction of such natural gas requires almost quantitative carbonoxide removal prior to the liquefaction step. The operator is thus facedwith the challenges of removing that amount of carbon oxides in a costeffective process and disposing it in an environmentally responsiblemanner. Subterranean injection of carbon oxides is known, but it isneither easy, nor foolproof, nor cheap. Carbon oxide reaction schemespresent other difficulties. An improved method of handling carbon oxidecontaining natural gas is desired.

SUMMARY OF THE INVENTION

The present integrated process is directed to removing carbon oxidesfrom a carbon oxide containing fluid. The integrated process is furtherdirected to methods for producing hydrogen for use in carbon oxidemitigation, in a thermally effective manner. In one embodiment, theprocess includes an electrolysis step for generating hydrogen for theprocess, and a thermal step for supplying heat to the electrolysis stepwhile converting carbon oxides. Accordingly, the process comprisesreacting carbon oxides with an active metal at an elevated temperatureand producing thermal energy; and supplying at least a portion of thethermal energy to an electrolysis process, and recovering hydrogen.

In one embodiment, the process includes a separation step for removingcarbon oxides from a carbon oxide containing fluid prior to treatment inthe thermal step. Accordingly, the process comprises separating a carbonoxide containing natural gas into a carbon oxide rich fluid and a carbonoxide depleted natural gas; contacting the carbon oxide rich fluid withan active metal at elevated temperature and producing thermal energy andmolecular carbon; supplying at least a portion of the thermal energy toan electrolysis process conducted at an elevated temperature, forproducing at least hydrogen from electrolysis of water or brine; andcontacting at least a portion of the hydrogen with carbon oxides to formhydrocarbons.

In one such embodiment, the carbon oxides which are converted to formhydrocarbons are produced from the carbon oxide containing natural gas.In another such embodiment, at least a portion of the hydrogen producedfrom the electrolysis of water is contacted with the carbon oxides inthe presence of a catalyst to form hydrocarbons. In another suchembodiment, the hydrocarbons that are formed include methane. In anothersuch embodiment, at least a portion of the carbon oxide depleted naturalgas is converted to a liquid phase.

In one embodiment, the process includes subjecting a carbon oxidecontaining fluid to hydrocarbon synthesis prior to a separation step.Accordingly, in one such embodiment, the process comprises supplying acarbon oxide containing natural gas, in combination with H₂ to ahydrocarbon synthesis zone; contacting the carbon oxide containingnatural gas and hydrogen in the presence of a catalyst in thehydrocarbon synthesis zone to form hydrocarbons and a carbon oxidereduced natural gas; supplying the hydrocarbons and carbon oxide reducednatural gas to a separation zone and recovering a carbon oxide richfluid and a carbon oxide depleted natural gas; contacting at least aportion of the carbon oxide rich fluid with an active metal at elevatedtemperature and producing thermal energy and molecular carbon; supplyingat least a portion of the thermal energy to an electrolysis processconducted at an elevated temperature, for producing at least hydrogenfrom electrolysis of water or brine; and contacting at least a portionof the hydrogen produced from electrolysis with carbon oxides to formhydrocarbons.

In one embodiment, carbon oxides are removed in the natural gas deliverysystem that conducts the natural gas from a geological formation inwhich it occurs to surface facilities for processing and handling. Thisembodiment comprises producing a carbon oxide containing natural gasfrom a geological formation through a natural gas delivery system;providing a reaction zone containing at least one catalyst suitable forhydrocarbon conversion in the natural gas delivery system; introducinghydrogen into the carbon oxide containing natural gas to form a reactionmixture; passing the reaction mixture over the catalyst in the reactionzone to convert at least a portion of the carbon oxides in the naturalgas; and producing a carbon oxide reduced natural gas.

In one embodiment, at least one catalyst suitable for hydrocarbonconversion is provided in a product manifold that transports natural gasfrom more than one well to surface facilities for processing andhandling.

In one embodiment, the process includes treating a carbon oxidecontaining natural gas in a hydrocarbon synthesis step, and using a fluegas to generate the thermal energy for the electrolysis to producehydrogen. Accordingly, the process comprises supplying a carbon oxidecontaining natural gas, in combination with H₂ to a hydrocarbonsynthesis zone; contacting the carbon oxide containing natural gas andhydrogen with a catalyst in the hydrocarbon synthesis zone to formhydrocarbons and a carbon oxide reduced natural gas; contacting a fluegas with an active metal at elevated temperature and producing thermalenergy and molecular carbon; supplying at least a portion of the thermalenergy to an electrolysis process conducted at an elevated temperature,for producing at least hydrogen from electrolysis of water or brine; andcontacting at least a portion of the hydrogen produced from electrolysiswith carbon oxides to form hydrocarbons. In one such embodiment, theprocess further comprises liquefying at least a portion of the carbonoxide reduced natural gas.

In one embodiment, the process for contacting a carbon oxide containingfluid with an active metal at elevated temperature in a combustion zoneof a reaction vessel, and producing hydrogen from electrolysis of wateror brine in an electrolysis zone of the reaction vessel, wherein atleast a portion of the heat generated within the combustion zoneprovides the thermal energy for maintaining the electrolysis zone at anelevated temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 through FIG. 7 illustrate embodiments of the process whichincludes reducing the carbon oxide content of natural gas.

DETAILED DESCRIPTION OF THE INVENTION

The present integrated process for producing hydrocarbons whileconverting carbon oxides involves the treatment of a gaseous fluid thatcontains carbon oxides. The process comprises an electrolysis step forconverting carbon oxides to molecular carbon; the converted carbonoxides are thus removed as a potential greenhouse gas emission source.While CO₂ is an important contaminant that is converted in the process,other carbon oxides are also treated and removed as described. Thecarbon oxides are gaseous oxides, including, for example, carbon dioxide(CO₂) and carbon monoxide (CO) or combinations thereof. In oneembodiment, carbon oxides contain in the range from 90 vol. % to 100vol. % CO₂. In one embodiment, carbon oxides comprise CO₂ and CO in avolumetric ratio in the range from 99.9:0.1 to 50:50. In one embodiment,the carbon oxides comprise CO₂ and CO in a volumetric ratio in the rangefrom 99.99:0.01 to 95:5. The carbon oxides are contained in a fluid thatis gaseous at ambient temperature and pressure.

The carbon oxide containing gaseous fluid that is treated containscarbon oxides in a broad concentration range, depending on the sourceand the local requirements of the process. Natural gas that is suitablefor treatment contains in the region of 1 vol. % to 75 vol. % carbonoxides. Other gases that are suitable for treatment, such as flue gas,contain in the range from 1 vol. % to 60 vol. % carbon oxides. In somecases, a suitable gas for treatment contains a diluent, such as an inertgas, added, for example, to moderate the temperature of the oxidationreaction. Alternatively, the carbon oxide containing gas stream isseparated into at least a carbon oxide depleted fluid and a carbon oxiderich fluid. The carbon oxide rich fluid, which contains, in oneembodiment, in the range from 30 vol. % to 100 vol. % carbon oxides, ispassed to the metal oxidation step. In embodiments, the carbon oxidecontaining fluid also contains one or more other acidic contaminants,including, for example, hydrogen sulfide, carbonyl sulfide, carbondisulfide, mercaptans, sulfides and aromatic sulfur compounds. Anexemplary carbon oxide containing fluid contains between 0 and 45 vol. %hydrogen sulfide. Another exemplary carbon oxide containing fluidcontains between 5 and 40 vol. % hydrogen sulfide. In one embodiment,the carbon oxide depleted fluid is converted to liquefied natural gas.

Origin of Carbon Oxides

Flue Gas

In one embodiment, a flue gas is an input gas to the process, the fluegas containing the oxidation products from oxidation of carbonaceousmaterial. Furnaces, boilers, and heaters, including process heaters, aresuitable sources of the flue gas. Industries that would benefit from theprocess include petrochemical, petroleum, crude oil and gas producing,heat generating and mining industries, and the like. In one embodiment,the flue gas is obtained from a power producing plant, such as a coalfired, or oil fired or natural gas fired power plant, a steel plant, apetrochemical plant, a refinery, a cement plant, or any other plant thatproduces a flue gas. In addition to the carbon oxides, the flue gas maycontain oxides of sulfur and nitrogen, including sulfur dioxide, nitricoxide and nitrogen dioxide.

Natural Gas

In one embodiment, the carbon oxides are present as a contaminant ofnatural gas. Natural gas, which contains methane and varying amounts ofheavier hydrocarbons, may be recovered from geological formations as amixture with carbon oxides and other contaminant gases. Natural gascontaining as much as 75 vol. % carbon oxides, or more, is known.Indeed, gases containing up to 100% carbon oxides may be treated by theprocess.

Carbon Oxide Containing Fluid

Carbon Oxide Separation and Concentration

In one embodiment, the carbon oxides are provided to the process incombination with flue gas or natural gas, without preliminaryseparation. In another embodiment, the carbon oxides are separated fromthe other gases with which they are associated. Various carbon oxideremoval processes are known. These include absorption processes such asthose using an amine solvent solution (e.g. methyl-diethanol amine andwater), cryogenic processes, adsorption processes such as pressure swingadsorption (PSA) and thermal swing adsorption (TSA), and membrane-basedprocesses.

Membrane Separation

Membranes with a high selectivity for acidic contaminants in the gaseousfluid, such as carbon dioxide and hydrogen sulfide, are known. Theselectivity is defined as the ratio of the acidic contaminantspermeability over the permeability of the hydrocarbons as measured insingle gas experiments. An exemplary membrane for use in the process hasa selectivity of between 10 and 200. Another exemplary membrane has aselectivity of between 20 and 150. A membrane of this type includes, forexample, a membrane chosen from a polyethylene oxide based membrane, apolyethylene oxide based membrane comprising block-copolymers, a crosslinked polyethylene oxide based membrane, a polyimide or polyaramidebased membrane, a cellulose acetate based membrane, a zeolite basedmembrane, a silica-alumina phosphate based membrane, such as SAPO-34, amicro-porous silica membrane or a carbon molecular sieve membrane.

Amine Separation

In an embodiment, the retentate from the membrane separation is furthercontacted with an amine solvent, in an amine separation step, forextracting at least a portion of the carbon oxides remaining the in theretentate into the amine solvent. Amine separation facilities for arewell known. An exemplary amine solvent is methyldiethanol amine. Thecarbon oxide containing fluid that is supplied to the separation processwill have a pressure between 30 and 120 bara. An exemplary separationprocess involves treating a carbon oxide containing fluid having apressure between 40 and 100 bara; a second exemplary separation processtreats a carbon oxide containing fluid having a pressure between 50 and90 bara. The carbon oxide containing fluid has a temperature between −30and 120° C. One exemplary fluid has a temperature between −20 and 100°C. A second exemplary fluid has a temperature between 0 and 50° C. Thecarbon oxide rich fluid that is produced from a membrane separation andsupplied to the metal oxidation step generally has a pressure between 1and 30 bara; an exemplary fluid has a pressure between 5 and 25 bara.

Metal Oxidation

In carrying out one step of the process, an active metal is reacted withcarbon oxides at an elevated temperature. During the reaction, theactive metal is converted to an oxide and the carbon oxides are reduced.In the case of carbon dioxide as the reactant, carbon monoxide andcarbon are reduced products. In the case of carbon monoxide as thereactant, carbon is the reduced product. While some carbon monoxide maybe produced during the reaction, the process is generally operated toconvert a high proportion of the carbon oxides to molecular carbon (i.e.solid carbon).

In one embodiment, the reactions of the metal with the carbon oxides maybe illustrated as follows. At least a portion of the carbon oxidescontained in the carbon oxide containing fluid is believed to react bythe following stoichiometry:CO₂+2M→2MO+C  (a)

Likewise, at least a portion of the carbon monoxide contained in thefluid, or that is generated during the metal oxidation step, is believedto form molecular carbon by the following stoichiometry:CO+M→MO+C  (b)wherein CO₂ and CO represent carbon dioxide and carbon monoxiderespectively, M represents a metal, MO represents a metal oxide and Crepresents molecular carbon. Alternatively, at least a portion of thecarbon dioxide contained in the fluid, or that is generated during themetal oxidation step, is believed to form CO by the followingstoichiometry:CO₂+M→MO+CO  (c)

The active metal that is suitable for the process is any metal thatreacts with carbon oxides with the generation of heat. In oneembodiment, the active metal is aluminium; in another embodiment,magnesium; in another embodiment, iron; in another embodiment, calcium;in another embodiment, zinc. In a further embodiment, the active metalis selected from the group consisting of aluminium, magnesium, iron,calcium, zinc, and combinations thereof. The active metal is provided tothe oxidation process as a pure metal or in a mixture, alloy or blendwith at least one other material, the other material having some, or inthe alternative no, activity for reacting with the carbon oxide. Themetal that is provided to the oxidation process is of a form that isconducive to reaction, e.g. a powder, a ribbon, a sheet, a foil, a rod,or a brick. Scrap metal is also a suitable source of the active metal.

To initiate the process, the reactive metal is heated to at least aninitiation temperature, at which the metal ignites in a fluid of flowingcarbon oxide containing gas. The ignition temperature depends on themetal, on the concentration of carbon oxides in the flowing gas fluid,and on the inlet temperature of the flowing gas fluid. Under someconditions, at least, the ignition temperature is above 500° C. In oneembodiment, the metal reacts with the carbon oxides at a temperature inthe range from 500° C. to 2000° C. In one embodiment, the metal reactswith the carbon oxides at a pressure in the range from 1 bara to 100bara (i.e. atmospheric pressure to 100 atmospheres pressure).

The metal oxidation step is exothermic, and, under some conditions atleast, high exothermic. At least a portion of the thermal energygenerated during the metal oxidation is recovered, for use in theelectrolysis step that is a part of the integrated process. In oneembodiment, the heat generated during oxidation is carried from thereaction by gas phase effluent from the oxidation step, at least aportion of which is exchanged with the electrolysis. Alternatively, theelectrolysis step is conducted within the metal oxidation reaction zone;thermal energy from oxidation is passed directly to electrolysis. Inanother embodiment, the water that is supplied to the electrolysisprocess passes first through the metal oxidation process for heating.

The metal oxidation step also forms molecular carbon, which is collectedfrom the oxidation step. In one embodiment, the molecular carbon passesfrom the reaction in the form of a powder, which is recovered using oneor more known gas/solid process, such as, for example, a filterseparation, a cyclone separation, an electrostatic separation, or acombination thereof.

Electrolysis

In one embodiment, the thermal energy generated in sequestering carbonoxides in the process is used by the process for generating hydrogen. Ineffect, the process for converting carbon oxides to hydrogen in themultistep process provides a method for converting a greenhouse gas intoa fuel or reaction feedstock, including a reaction feedstock for theproduction of additional hydrocarbonaceous products. Alternative knownor future developed heat sources may be used and are within the scope ofthe invention. This could include, e.g., solar energy or heat from otherindustrial processes. Alternative known or future developed sources ofhydrogen are also within the scope of the invention.

At least a portion of the thermal energy generated during metaloxidation is provided to an electrolysis step, where electrolysisinvolves using an external circuit to produce a chemical change. Theelectrolysis is conducted at elevated temperature to exploit anefficiency improvement with increasing temperature. In one embodiment,the high temperature electrolysis involves the disassociation of waterinto oxygen and hydrogen; the electrolysis is suitably conducted at atemperature such that the water participates in the electrolysisreactions in the vapor phase. In one embodiment, the electrolysis stepis conducted at a temperature of greater than 100° C.; in anotherembodiment, the electrolysis step is conducted at a temperature in therange from 100° C. to 850° C. Using the thermal energy for other knownor future developed uses, e.g., rankine cycle heat recovery, is withinthe scope of the invention.

Water Electrolysis

In one embodiment, water is a feedstock to the electrolysis process;products include H₂ and O₂ from the disassociation of the water. Becausewater electrolysis is increasingly endothermic with temperature,electricity demand can be significantly reduced, if the formation ofhydrogen takes place at high temperatures. Product oxygen recovered fromelectrolysis may be used for oxidation within the process, may beremoved from the process for other uses, or may be vented.

CO₂ Electrolysis

In one embodiment, carbon dioxide is a feedstock to the electrolysisprocess; products include CO and O₂. The CO is useful, for example, as afeedstock to a hydrocarbon synthesis process. In one embodiment,methanol is a product of the synthesis process. In one embodiment,methane is a product. In one embodiment, higher hydrocarbons, includinghydrocarbons having carbon numbers from C₂ (e.g. ethane) to C₁₀₀comprise at least a portion of the products from hydrocarbon synthesis.In one embodiment, diethyl ether is a product. In one embodiment,alcohols comprise at least a portion of the products. In one embodiment,the hydrocarbon synthesis process is a Fischer Tropsch process.

H₂O+CO₂ Electrolysis

In one embodiment, a mixture of water and CO₂ is a feedstock to theelectrolysis process; products include CO and H₂. In another embodiment,electrolysis of a mixture of water and CO₂, in the presence of acatalyst, produces hydrogen and methane. In one embodiment, the catalystcomprises nickel.

Chloroalkali Electrolysis

In one embodiment, the hydrogen produced for the hydrocarbon synthesisstep of the integrated process is generated by a chloroalkalielectrolysis process. Chloroalkali electrolysis is generally conductedin a membrane cell or a diaphragm cell. In the membrane cell, the anodeand cathode are separated by an ion-permeable membrane. Saturated brineis fed to the compartment with the anode. A DC current is passed throughthe cell and the NaCl splits into its constituent components. Themembrane passes Na+ ions to the cathode compartment, where it formssodium hydroxide in solution. The membrane allows only positive ions topass through to prevent the chlorine from mixing with the sodiumhydroxide. The chloride ions are oxidized to chlorine gas at the anode,which is collected, purified and stored. Hydrogen gas and hydroxide ionsare formed at the cathode. A membrane cell is used to prevent thereaction between the chlorine and hydroxide ions.

In the diaphragm cell process, there are two compartments separated by apermeable diaphragm, often made of asbestos fibers. Brine is introducedinto the anode compartment and flows into the cathode compartment.Similarly to the Membrane Cell, chloride ions are oxidized at the anodeto produce chlorine, and at the cathode, water is split into causticsoda and hydrogen. The diaphragm prevents the reaction of the causticsoda with the chlorine, A diluted caustic brine leaves the cell. Thechlorine contains oxygen and must often be purified by liquefaction andevaporation.

Hydrocarbon Synthesis

In the integrated process, hydrogen is used for hydrocarbon synthesis,in which methane and/or higher hydrocarbons are synthesized fromreaction of H₂ with CO and CO₂. In one embodiment, H₂ used in theprocess is produced from one of a number of sources, including methane(and higher hydrocarbon) reforming, refinery processing andelectrolysis. Applications of the integrated process that include anelectrolysis step employ at least a portion of the hydrogen generatedfrom electrolysis in the hydrocarbon synthesis step.

Carbon oxides that are used as a reactant for hydrocarbon synthesis ispresent in the flue gas or natural gas that is contaminated with carbonoxides (i.e., the carbon oxide containing fluid). In one embodiment, thecarbon oxide containing fluid is contacted with hydrogen in the presenceof a catalyst to form hydrocarbons and to reduce the amount of carbonoxides in the fluid. Fluids having a carbon oxide concentration in therange from 5 vol. % to 100 vol. % are suitable as feedstocks for thehydrocarbon synthesis step. In another embodiment, the carbon oxidecontaining fluid is treated in a separation step, which removes at leasta portion of the carbon oxides into a carbon oxide rich fluid that isreacted with hydrogen in the hydrocarbon synthesis step.

CO₂ is generally a major component of carbon oxide contamination ofnatural gas; CO is generally a minor component, though the concentrationof CO in flue gas may reach percent levels in some situations for whichthe present integrated process finds applicability. CO for thehydrocarbon synthesis step is generally made available to the process incombination with hydrogen as syngas. Syngas is produced during partialoxidation of carbonaceous material, including methane. In oneembodiment, the integrated process includes a methane reformer forproducing syngas by partial oxidation of natural gas for use inhydrocarbon synthesis and the capture and conversion of carbon oxide.Alternatively, carbon monoxide is recovered from the natural gas, andcombined with hydrogen to form the syngas.

Sabatier Reaction

In one embodiment of the integrated process, hydrogen is caused to reactwith CO₂ in a so-called Sabatier reaction to form hydrocarbons,including methane. The reaction is facilitated by the presence of acatalyst; catalysts comprising nickel, ruthenium or mixtures of the twoare suitable for use in the hydrocarbon synthesis step. Some usefulcatalysts include an oxide substrate.

In one embodiment, the hydrocarbon synthesis step occurs at a reactiontemperature in the range from 150° C. to 500° C.

The hydrocarbon synthesis reaction is exothermic; in one embodiment,thermal energy generated during the synthesis reaction is passed to theelectrolysis reaction to support maintaining the elevated temperatureelectrolysis process.

Water Gas Shift Reaction

The water gas shift reaction, which involves the reaction of CO with H₂Oto form CO₂ and H₂, is useful in the process for preparing reactants tobe used in the hydrocarbon synthesis step. In one embodiment, CO isinjected into a natural gas that contains water vapor to increase theamount of hydrogen present in the natural gas. Catalysts such astransition metals, transition metal oxides (e.g. Fe3O4) and Raney copperare suitable catalysts for the process. In one embodiment, a two stagereaction sequence is employed, with a first high temperature stage at350° C. in the presence of an iron oxide catalyst promoted with chromiumoxide, and a second low temperature stage in the presence of a zincoxide on aluminium oxide catalyst.

CO₂ Conversion in a Natural Gas Delivery System.

In one embodiment, a carbon dioxide containing natural gas is producedfrom a geological formation and passes to surface processing andhandling at some location from the production well. A natural gasdelivery system includes the equipment and means, including tubing andvalving, for conducting natural gas from the geological formation tosurface processing and handling facilities. The delivery tubing andsystem for delivering the natural gas from the geological formation, forfinal cleanup and purification, comprises a reaction zone for convertingat least a portion of the carbon dioxide contained in the natural gas,via a hydrocarbon synthesis reaction.

In one embodiment, the reaction zone is provided to remove CO₂ as anenvironmental greenhouse gas from the natural gas. In one embodiment,the reaction zone is positioned within the natural gas delivery systemat a location between the geological formation, where the natural gasenters the tubing of the delivery system, and facilities on the earth'ssurface for processing and handling the produced natural gas.

In one embodiment, at least a portion of the CO₂ is converted in thereaction zone into hydrocarbons, such as methane, in a hydrocarbonsynthesis step. A material having catalytic activity for hydrocarbonsynthesis is provided in the reaction zone to facilitate the synthesis.In one embodiment, the reaction zone contains a hydrocarbon synthesiscatalyst for reacting CO₂ with H₂ to form methane. In one suchembodiment, the catalyst is nickel; in another embodiment, ruthenium; inanother embodiment, nickel-ruthenium. In another embodiment, reaction ofCO and H₂ produces principally normal paraffin and alcohol products.Cobalt or iron, with or without a platinum promoter, are suitablecatalysts. In one embodiment, the reaction involves a Fischer Tropschreaction, for converting CO (or CO2 that is interconverted to CO) andhydrogen to paraffinic hydrocarbons and alcohols.

The water gas shift reaction, which interconverts water, H₂ and thecarbon oxides is suitable for shifting the balance of reactants withinthe natural gas. The pressure and temperature of the reaction zonewithin the delivery system, at which the catalytic reaction occurs, issupplied by the conditions of the geological formation from which thenatural gas is produced.

In one embodiment, a single reaction zone is provided in the process. Inanother embodiment, multiple reaction zones are provided, eachcontaining a catalyst intended for a different reaction, whether it be aCO₂+H₂ reaction to yield methane, a CO+H₂ reaction to yield alcohols andparaffins, or whether it be a water gas shift catalyst forinterconverting water, H₂, CO and CO₂. Multiple reaction zones areeither adjacent each other, or separated. In one embodiment, thecatalyst is coated or plated directly on the inner wall of the tubing inthe delivery system. The tubing in a typical natural gas delivery systemmay be of considerable length; over the course of the passage of thenatural gas through the delivery system, there is sufficient contactbetween the carbon dioxide molecules in the natural gas and the walls ofthe delivery tubing to facilitate the conversion of at least a portionof the carbon dioxide to hydrocarbons.

In another embodiment, the reaction zone within the natural gas deliverysystem includes a honeycomb monolith, with catalytically active metalsbeing deposited on the interior channels of a honeycomb monolithic.Generally a monolith substrate has a large surface area to facilitatethe catalytic conversion process. A honeycomb structure containsnumerous channels, usually running parallel to each other along thelength of the substrate. The channel width varies, often depending onthe substrate material and applications for which it is used. Thesechannels allow the natural gas containing the carbon dioxide to flowfreely through the monolith with a minimum of pressure drop. While thenatural gas flows through the channels of the substrate and contacts thecatalytic metals deposited thereon, the carbon dioxide molecules areconverted into hydrocarbons molecules via chemical reactions.

In another embodiment, the catalytic metals are deposited on a staticmixer that is installed in the tubing in the natural gas deliverysystem.

In another embodiment, catalytic metals are deposited on substratebeads, which are introduced into the reaction zone within a natural gasdelivery system for converting the carbon dioxide contained therein.Typical shapes of the beads includes flutes, cylinders and spheres, withan effective diameter in the region from 0.01 inch to 1 inch. In oneembodiment, the beads are sized to permit lifting, fluidization ortransport of the beads in the flowing natural gas within the deliverysystem. In another embodiment, the beads are sized and positioned suchthat at least a portion of them are fixed in place, and the natural gascontaining the carbon dioxide is permitted to flow around the individualbeads and through the reaction zone containing the beads.

Example 1

In the exemplary process illustrated in FIG. 1, a carbon oxidecontaining fluid (110) is passed to a metal oxidation unit (120) forconverting the carbon oxides to molecular carbon, and/or CO₂ to CO,while oxidizing an active metal (130) to form an oxide form of themetal. In one embodiment, the active metal comprises aluminum. Inanother embodiment, the active metal comprises magnesium. In oneembodiment, the carbon oxide containing fluid is a natural gas; inanother embodiment, a flue gas. In one embodiment, the carbon oxidecontaining fluid comprises CO₂; in another embodiment, it comprises CO;in another embodiment, it comprises a combination of CO₂ and CO. Aninert diluent stream (140) may optionally be added to the carbon oxidecontaining fluid (110), prior to introducing the fluid to the oxidationstep. The metal oxidation step produces thermal energy (150), along withmetal oxide (160) and molecular carbon and/or CO, (170) products.

In the process, at least a portion of the thermal energy (150) is passedto an electrolysis process step (180). In one embodiment, theelectrolysis step (180) is a high temperature electrolysis forelectrolyzing water (185) into its elemental components, hydrogen (190)and oxygen (195). In another embodiment (not shown), the electrolysisstep involves an chloralkali electrolysis of brine, to form hydrogen,sodium hydroxide and at least one chlorine containing fluid. Electricalenergy (199) is also passed to the electrolysis step for conducting theelectrolysis process.

Example 2

In the exemplary process illustrated in FIG. 2, a carbon oxidecontaining fluid (110) is passed to a separation step (210), forrecovering at least a portion of the carbon oxides. At least two streamsare produced in the separation step: a carbon oxide rich fluid (220)which contains at least a portion of the separated carbon oxides, and acarbon oxide depleted (230) fluid from which at least a portion of thecarbon oxides have been removed. In one embodiment, the carbon oxidedepleted fluid (230) is a natural gas. In one embodiment, the carbonoxide depleted natural gas (230) is passed to a liquefaction process forconverting the natural gas to liquefied natural gas. In one embodiment,the separation step (210) includes a membrane separation; in anotherembodiment, an amine separation; in another embodiment, a combination ofa membrane separation and an amine separation.

The carbon oxide rich fluid (220) is supplied to a metal oxidation step(120) for converting the carbon oxides in the fluid to molecular carbon,and/or CO₂ to CO. When maintained at a temperature above the ignitiontemperature, an active metal (130) reacts with carbon oxides in a highlyexothermic reaction, forming at least an oxide (160) of the active metaland reducing the carbon oxides to molecular carbon and/or CO (170).Excess energy beyond that required to maintain the reaction in the metaloxidation step is available for use elsewhere in the integrated process.In the process, therefore, at least a portion of the thermal energy(150) generated during metal oxidation is passed to an electrolysisprocess step (180). In one embodiment, the electrolysis step (180) is ahigh temperature electrolysis for electrolyzing water (185) into itselemental components, hydrogen (190) and oxygen (195). In anotherembodiment (not shown), the electrolysis step involves a chloroalkalielectrolysis of brine, to form hydrogen, sodium hydroxide and at leastone chlorine containing fluid. Electrical energy (199) is also passed tothe electrolysis step for conducting the electrolysis process.

Hydrogen (190) generated in the electrolysis process (180) is recoveredfor other uses in the integrated process. In one embodiment, theintegrated process comprises a hydrocarbon synthesis step (240), forconverting the hydrogen (190) and carbon dioxide (245) intohydrocarbons, e.g. methane. Carbon oxides from one or more of a numberof sources, both from within and from outside of the integrated process,are suitable as a feedstock for the hydrocarbon synthesis step,including, for example, a portion of the carbon oxide containing fluid(110), a portion of the carbon oxide rich fluid (220), a portion of thecarbon oxide depleted fluid (230), a separate carbon oxide containingfluid (245) produced during the separation step (210), a carbon oxidecontaining natural gas, and combinations thereof. During the catalyticconversion of CO₂ and H₂ in the hydrocarbon synthesis step (240), atleast one hydrocarbon product (260) is produced, along with a waterbyproduct stream (250). In one embodiment, CO₂ react with H₂ over anickel catalyst, a ruthenium catalyst, or a nickel-ruthenium catalyst toform methane. In one embodiment, at least a portion of the thermalenergy (270) from the exothermic reactions during hydrocarbon synthesis(240) is passed to the electrolysis step (180).

Example 3

In the exemplary process illustrated in FIG. 3, a carbon oxidecontaining fluid (110), such as a natural gas, is passed to ahydrocarbon synthesis step (240) for converting at least a portion ofthe carbon dioxide contained therein into hydrocarbons (260) (e.g.methane) via reaction with hydrogen (190). At least a portion of thehydrogen (190, 290) which is supplied to the hydrocarbon synthesis step(240) is produced in an electrolysis step (180). In one embodiment,additional hydrogen (290) for synthesis is supplied from one or moreadditional sources (280), either from within or from outside of theintegrated process.

In the embodiment illustrated in FIG. 3, methane that is formed duringhydrocarbon synthesis is passed to a separation step (210) incombination with a carbon oxide reduced natural gas (310). In theseparation step (210), at least a portion of the carbon oxides thatremain in the natural gas following the hydrocarbon synthesis step (240)are separated into a carbon oxide rich fluid (220); a carbon oxidedepleted fluid (230) is also recovered. In one embodiment, the carbonoxide depleted fluid comprises natural gas, and the carbon oxidedepleted natural gas (230) is passed to a liquefaction process forconverting the natural gas to liquefied natural gas.

The carbon oxide rich fluid (220) is supplied to a metal oxidation step(120) for converting the carbon oxides in the fluid to molecular carbon,and/or CO₂ to CO (170), and further converting at least one active metal(130) to at least one metal oxide (160). In the process, at least aportion of the thermal energy (150) generated during metal oxidation ispassed to an electrolysis process step (180). In the embodimentillustrated in FIG. 3, thermal energy (270) generated during hydrocarbonsynthesis is also passed to the electrolysis process step (180). In oneembodiment, the electrolysis step (180) is a high temperatureelectrolysis for electrolyzing water (185) into its elementalcomponents, hydrogen (190) and oxygen (195). In another embodiment (notshown), the electrolysis step involves a chloroalkali electrolysis ofbrine, to form hydrogen, sodium hydroxide and at least one chlorinecontaining fluid. Electrical energy (199) is also passed to theelectrolysis step for conducting the electrolysis process.

Example 4

FIG. 4 illustrates a hydrocarbon synthesis reaction zone (410) in anatural gas (or a crude oil containing natural gas) production system.In the exemplary process illustrated in FIG. 4, a carbon oxidecontaining natural gas (420) is produced from a geological formationthrough perforations (430) in a well casing (440) and into well tubing(450). A reaction zone (460) for converting at least a portion of thecarbon oxides contained in the natural gas is included in the welltubing. The reaction zone (460) includes a catalyst for the CO₂conversion. In one embodiment, the catalyst is plated or coated to theinner wall of the well tubing; in another embodiment, it is provided onbeads within a fixed or fluidized catalyst bed; in another embodiment,it is included in a fixed bed static mixer within the well tubing; inanother embodiment, it is included in a monolith structure within thewell tubing; in another embodiment, it is provided to the well tubing inany combination of these.

The carbon oxide content in the natural gas is reduced by conversion tohydrocarbons in one or a series of chemical conversion processes. In oneembodiment, reaction of CO₂ with H₂ is forms methane. Nickel andruthenium, taken alone or in combination, are suitable catalysts. Inanother embodiment, reaction of CO and H₂ produces principally normalparaffin and alcohol products. Cobalt or iron, with or without aplatinum promoter, are suitable catalysts. The water gas shift reaction,which interconverts water, H₂ and the carbon oxides is suitable forshifting the balance of reactants within the natural gas.

H₂, CO or syngas (mixture of H₂ and CO (470)) is prepared in surfacefacilities is passed to the well tubing (450) that conducts the naturalgas to the reaction zone (460) containing the catalyst. In oneembodiment, at least a portion of the hydrogen is generated byelectrolysis.

The pressure and temperature of the H₂/natural gas blend is determined,at least in part, by the reservoir conditions from which the natural gasoriginates. In the reaction zone the CO₂ in the natural gas reacts inthe presence of the catalyst to form reaction products, e.g. methane.The product methane blends with the natural gas and the CO₂concentration of the natural gas is reduced.

In one embodiment, natural gas leaving the reaction zone (460) passes toadditional separation steps for farther separation of remaining carbonoxides in the natural gas.

Example 5

FIG. 5 illustrates a hydrocarbon synthesis reaction zone in the deliverysystem of a natural gas (or a crude oil containing natural gas)production system. In the exemplary process illustrated in FIG. 5, acarbon oxide containing natural gas (420) is produced from a geologicalformation through performations (430) in a well casing (440) and intowell tubing (450). From there the produced natural gas (510) from thewell tubing combines with natural gas (520) produced in other wells in aproduct manifold (530), and the combination passes to a reaction zone(560) in the delivery tubing for converting at least a portion of thecarbon oxides contained in the natural gas.

The reaction zone (560) includes a catalyst for the CO₂ conversion. Inone embodiment, the catalyst is plated or coated to the inner wall ofthe well tubing; in another embodiment, it is provided on beads within afixed or fluidized catalyst bed; in another embodiment, it is includedin a fixed bed static mixer within the well tubing; in anotherembodiment, it is included in a monolith structure within the welltubing; in another embodiment, it is provided to the well tubing in anycombination of these.

The carbon oxide content in the natural gas is reduced by conversion tohydrocarbons in one or a series of chemical conversion processes. In oneembodiment, reaction of CO₂ with H₂ is forms methane. Nickel andruthenium, taken alone or in combination, are suitable catalysts. Inanother embodiment, reaction of CO and H₂ produces principally normalparaffin and alcohol products. Cobalt or iron, with or without aplatinum promoter, are suitable catalysts. The water gas shift reaction,which introconverts water, H₂ and the carbon oxides is suitable forshifting the balance of reactants within the natural gas.

H₂, CO or syngas (mixture of H₂ and CO (470)) is prepared in surfacefacilities is passed to the well tubing (450) that conducts the naturalgas to the reaction zone (560) containing the catalyst. In oneembodiment, at least a portion of the hydrogen is generated byelectrolysis.

The pressure and temperature of the H₂/natural gas blend is determined,at least in part, by the reservoir conditions from which the natural gasoriginates. In the reaction zone the CO₂ in the natural gas reacts inthe presence of the catalyst to form reaction products, e.g. methane.The product methane blends with the natural gas and the CO₂concentration of the natural gas is reduced.

In one embodiment, natural gas leaving the reaction zone passes toadditional separation steps for further separation of remaining carbonoxides in the natural gas.

Example 6

In the exemplary process illustrated in FIG. 6, a carbon oxidecontaining natural gas (610) is passed over a hydrocarbon synthesiscatalyst in a hydrocarbon synthesis step (240), for converting at leasta portion of the carbon oxides in the natural gas to hydrocarbons. Anexemplary hydrocarbon product in this reaction is methane. Thermalenergy (270) produced during hydrocarbon synthesis is passed to anelectrolysis step (180). Natural gas (620) depleted in carbon oxides isproduced from the hydrocarbon synthesis. In one embodiment, the carbonoxide depleted natural gas (620) is passed to a liquefaction process forconverting the natural gas to liquefied natural gas. At least a portionof the hydrogen (190) which is provided to the hydrocarbon synthesisstep is generated from electrolysis (180) of water or a brine solution(185). At least a portion of the thermal energy (150) for operating theelectrolysis process (180) at elevated temperature is provided from areaction of flue gas (630) over an active metal (130) in a metaloxidation process (120). The carbon oxides in the flue gas react withthe active metal, forming a metal oxide and capturing the carbon in thecarbon oxides as molecular carbon and/or CO (170). In one embodiment, aportion of the thermal energy (270) generated from the hydrocarbonsynthesis reaction (240) is provided to the electrolysis process (180).

Example 7

In the exemplary process illustrated in FIG. 7, a carbon oxidecontaining fluid (110) is passed over an active metal (130) in a metaloxidation step (120), for converting the metal to a metal oxide (160),and for capturing the carbon in the carbon oxides as molecular carbon,and/or CO₂ to CO (170). Integral in the metal oxidation process is anelectrolysis process (180) for the high temperature electrolysis ofwater or brine. Heat generated in the metal oxidation step is directlyavailable to the electrolysis step. In one embodiment, the oxidation andelectrolysis are conducted in a shell and tube system, with one of theoxidation or electrolysis being conducted on the shell side of thesystem, and the other process, oxidation or electrolysis, beingconducted within the tubes of the system. Hydrogen (190) generated inthe electrolysis portion of the integral process is available forreacting with other portions of carbon oxides in a hydrocarbon synthesisprocess to generate additional amounts of methane in the process.

What has been described above includes examples of the presentinvention. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe present invention, but one of ordinary skill in the art mayrecognize that many further combinations and permutations of the presentinvention are possible. Accordingly, the present invention is intendedto embrace all such alterations, modifications and variations that fallwithin the spirit and scope of the appended claims. Furthermore, to theextent that the term “includes” is used in either the detaileddescription or the claims, such term is intended to be inclusive in amanner similar to the term “comprising” as that term is interpreted as atransitional word in a claim.

What is claimed is:
 1. A process for producing hydrocarbons from carbonoxides, comprising: a) a reacting a first carbon oxides with an activemetal at an elevated temperature and producing thermal energy; b)supplying at least a portion of the thermal energy to an electrolysisprocess, and recovering hydrogen; and c) contacting at least a portionof the hydrogen with a second carbon oxides to form hydrocarbons.
 2. Theprocess of claim 1, wherein the active metal is selected from the groupconsisting of magnesium, aluminium, iron, calcium, and zinc.
 3. Theprocess of claim 1, wherein the active metal is aluminium.
 4. Theprocess of claim 1, further comprising reacting the first carbon oxideswith an active metal at a temperature of greater than 500° C.
 5. Theprocess of claim 1, wherein the first carbon oxides comprise in therange from 90 vol. % to 99.99 vol. % CO₂.
 6. The process of claim 1,further comprising producing molecular carbon from the reaction of thefirst carbon oxides with the active metal.
 7. The process of claim 1,wherein the first carbon oxides comprises CO₂, and the process furthercomprising producing CO from the reaction of CO₂ with the active metal.8. The process of claim 1, wherein the electrolysis process involves theelectrolysis of water or brine.
 9. The process of claim 1, wherein theelectrolysis process involves the electrolysis of water or brine at atemperature in the range from 100° C. to 850° C.
 10. The process ofclaim 1, wherein the first carbon oxides are recovered from carbon oxidecontaining natural gas.
 11. The process of claim 1, wherein the secondcarbon oxides are contained in carbon oxide containing natural gas formhydrocarbons.
 12. The process of claim 1, further comprising separatinga natural gas that contains carbon oxides into at least a carbon oxiderich fluid and a carbon oxide depleted natural gas; and reacting thecarbon oxide rich fluid with the active metal.
 13. The process of claim12, further comprising contacting at least a portion of the hydrogenwith a portion of the carbon oxide rich fluid to form hydrocarbons. 14.The process of claim 12, wherein the carbon oxide depleted natural gascontains less than 1 vol. % carbon oxides.
 15. The process of claim 12,further comprising passing the carbon oxide depleted natural gas to aliquefaction process.
 16. A process for producing hydrocarbons fromcarbon oxides, comprising: a) separating a carbon oxide containingnatural gas into a carbon oxide rich fluid and a carbon oxide depletednatural gas; b) contacting the carbon oxide rich fluid with an activemetal at elevated temperature and producing thermal energy and molecularcarbon; c) supplying at least a portion of the thermal energy to anelectrolysis process conducted at an elevated temperature, for producingat least hydrogen from electrolysis of water or brine; d) contacting atleast a portion of the hydrogen produced from electrolysis with carbonoxides to form hydrocarbons.
 17. The process of claim 16, wherein thehydrocarbons that are formed include methane.
 18. The process of claim16, wherein the active metal is selected from the group consisting ofmagnesium, aluminum, iron, calcium, and zinc.
 19. The process of claim16, further comprising passing the carbon oxide depleted natural gas toa liquefaction process.
 20. The process of claim 16, further comprisingcontacting at least a portion of the hydrogen with a portion of thecarbon oxide rich fluid to form hydrocarbons.